Generally, a cathode ray tube is provided with a panel where a phosphorescent layer is formed and a shadow mask is attached; a funnel where, a graphite is layered at the inside and outside surface; and a neck where an electron gun is received and a deflection yoke is attached to its periphery. The deflection yoke is provided with a pair of separators made of a resin; a horizontal deflecting coil which is attached to the inside surface; and a vertical deflecting coil which is attached to its outside surface.
The horizontal and vertical deflecting coils generate horizontal and vertical deflecting magnetic fields, in order to deflect an electron beam emitted from the electron gun to the screen corner. The horizontal and vertical deflecting coils are formed by the winding of a coil.
The deflected electron beam strikes the phosphorescent layer so as to reproduce the picture. However, after deflecting, the fields generated in the horizontal and vertical coils of the deflection yoke for deflecting the electron beam do not remain at each coil but flow out, so that unnecessary leaking magnetic fields range over the whole front face of a screen and are harmful to the human body as well. Accordingly, in a conventional ST (saddle toroidal) type deflection yoke, current is supplied with the coils wound on the periphery of the panel, so that reverse magnetic fields incurred therefrom reduce the leaking magnetic fields generated from the outside.
While the vertical deflecting coil causes little leaking the magnetic field is not harmful to the health. However, the horizontal deflecting coil produces much leaking and the magnetic field is harmful to the human body. The above reverse magnetic field acts against the horizontal deflecting coil to reduce the leaking magnetic field. However, in an improved SS (saddle saddle) type deflection yoke, current which can produce the magnetic field of the direction contrary to that from the horizontal deflecting coil is applied to a member for preventing the leaking magnetic field provided with a predetermined type bobbin fixed on the deflection yoke body and the magnetic body formed by winding the coils inserted in the bobbin, so that the reverse magnetic field generated therefrom can diminish the leaking magnetic field from the horizontal deflecting coil.
The deflection yoke to which the leaking magnetic field preventing member is applied is disclosed in U.S. Pat. No. 5,017,900. As shown in FIG. 8, a pair of cancellation coils 51, 51' installed in the vertical and horizontal direction opposite each other along the imaginary axis passing the central axis of a core 50 are arranged in the vicinity of a front end section of the vertical deflection coils 52, 52'. The cancellation coils 51, 51' are mounted in such a way that their central axis crosses the central axis of the core 50 at an angle .theta.. These cancellation coils 51, 51' are connected either in series or in parallel with the horizontal deflection coils 53, 53' and, also, each is wound on the magnetic body.
As shown in FIG. 9, U.S. Pat. No. 4,853,588 proposes the deflection yoke 50 that auxiliary coils 54, 54' are connected in series or in parallel to the horizontal deflection coils 55, 55' to generate the cancelling magnetic field which suppresses part of the externally leaking magnetic field radiated from the deflection yoke. However, these auxiliary coils 54, 54' are wound on the magnetic body as well.
As described above, the coils 51, 51', 54, 54' are wound on the magnetic body and the reverse magnetic field generated therefrom reduces the leaking magnetic field. However, the strong magnetic field radiated from the magnetic body itself diminishes the leaking magnetic field and at the same time, has an effect on the deflecting angle of the beam so as to cause the picture introversion of about 25 .mu.m. The use of the magnetic body results in a relatively high production cost.